Small readability improvements in Parser

Also add a test for a parser with no data

src/parser.cpp

@@ -18,7 +18,7 @@ Parser::Parser(std::istream& in) : Parser() { Load(in); }
 Parser::~Parser() = default;
 
 Parser::operator bool() const {
-  return m_pScanner.get() && !m_pScanner->empty();
+  return m_pScanner && !m_pScanner->empty();
 }
 
 void Parser::Load(std::istream& in) {
@@ -27,7 +27,7 @@ void Parser::Load(std::istream& in) {
 }
 
 bool Parser::HandleNextDocument(EventHandler& eventHandler) {
-  if (!m_pScanner.get())
+  if (!m_pScanner)
     return false;
 
   ParseDirectives();
@@ -43,11 +43,7 @@ bool Parser::HandleNextDocument(EventHandler& eventHandler) {
 void Parser::ParseDirectives() {
   bool readDirective = false;
 
-  while (1) {
-    if (m_pScanner->empty()) {
-      break;
-    }
-
+  while (!m_pScanner->empty()) {
     Token& token = m_pScanner->peek();
     if (token.type != Token::DIRECTIVE) {
       break;
@@ -113,15 +109,11 @@ void Parser::HandleTagDirective(const Token& token) {
 }
 
 void Parser::PrintTokens(std::ostream& out) {
-  if (!m_pScanner.get()) {
+  if (!m_pScanner) {
     return;
   }
 
-  while (1) {
-    if (m_pScanner->empty()) {
-      break;
-    }
-
+  while (!m_pScanner->empty()) {
     out << m_pScanner->peek() << "\n";
     m_pScanner->pop();
   }

test/mock_event_handler.h

@@ -1,8 +1,11 @@
 #include "yaml-cpp/emitterstyle.h"
 #include "yaml-cpp/eventhandler.h"
+#include "yaml-cpp/mark.h"
 
 #include "gmock/gmock.h"
 
+#include <string>
+
 namespace YAML {
 
 class MockEventHandler : public EventHandler {

test/parser_test.cpp

@@ -0,0 +1,16 @@
+#include "yaml-cpp/parser.h"
+#include "mock_event_handler.h"
+#include "gtest/gtest.h"
+
+using YAML::Parser;
+using YAML::MockEventHandler;
+using ::testing::StrictMock;
+
+TEST(ParserTest, Empty) {
+    Parser parser;
+
+    EXPECT_FALSE(parser);
+
+    StrictMock<MockEventHandler> handler;
+    EXPECT_FALSE(parser.HandleNextDocument(handler));
+}